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Full text of "Text Book Of Mechanical Engineering"

556

Laws and Exceptions.

Morin's experiments are not true for very heavy loads or at
high velocities with much abrasion.    For the first, Ball gives

Fn = -9 + -266 P

for wood on wood, and the relation is set out in Fig. 571, the
dotted  line   shewing the result  of the  ordinary formula with

As regards velocity, at the Brighton brake trials, 1878, the
following results were obtained when the static coefficient was -242.

Vel. ft. per sec.
	ju between brake and wheel.
	fji between wheel and rail.

80
	*io6
	

50
	153
	'065

40
	"171
	07

20
	'213
	072

IO
	242
	-088

near rest
	242
	'242